In suction rolls in paper machines, the wear of seals has constituted a rather significant problem. This problem has been emphasized in particular because it has been a general aim of seal constructions to obtain longer servicing intervals. The seals in a suction roll divide the interior of the roll mantle appropriately into vacuum chambers, and by means of a vacuum passed into these vacuum chambers, a suction effect is applied through holes formed in the roll mantle to the paper web running over an outer face of the roll mantle in order that the web should remain on the face of the roll mantle in the desired manner and over a desired circumferential distance of the suction roll. The seals are loaded against the inner face of the roll mantle. In an attempt to obtain an efficient and well-sealed suction roll, in earlier constructions, the seals in the suction roll were pressed, for example by means of compressed air, against the inner face of the roll mantle. The compression force was maintained constantly throughout operation of the suction roll which resulted in quite rapid wear of the seals. Moreover, a high compression force required water lubrication of the seals with abundant quantities of water. Further, owing to the high compression force, the power consumption of the sealing construction was considerable.
In view of eliminating this problem of wear, in the current assignee's earlier Finnish Patent Application No. 934909 (which corresponds to U.S. Pat. No. 5,580,424, the entire specification of which is incorporated by reference herein), the seals were not loaded constantly against the inner face of the roll mantle of the suction roll. Rather, the seals were provided with locking means so that initially the seal was pressed against the inner face of the roll mantle, and after a vacuum had been generated in the vacuum chamber defined by the seals, the seal was locked in its holder. Then it was possible to eliminate the load with which the seals were pressed against the inner face of the roll mantle while maintaining the seal in pressing engagement with the inner face of the roll mantle. In this manner, the wear of the seals could be reduced substantially, compared with the prior art constructions, and it was often even possible to eliminate the water lubrication of the seals. However, this earlier construction of the current assignee involved a quite substantial problem in that, in order for the desired sealing effect to be provided, the manufacturing tolerances of the seal construction were very small. Owing to these small tolerances, a detrimental consequence could be sticking of the seal in its position, as a result of which the desired sealing effect was not produced. It is another quite noticeable problem or drawback of this construction that the seal construction with the holders included in it was a rather exceptional, non-conventional construction, so that when this construction is applied in a suction roll, the entire seal construction with all of its components had to be changed to suit this specific seal construction.